what is impact evaluation?

Thanks to google and a question raised in my program evaluation class, here are some short definitions and links to more elaboration. As I said in class, impacts sound like outcomes to me (perhaps longer term ones), but I see that the term is appropriated by the causation through experimentation evaluation crowd.

****************************************************

Impact evaluation assesses the changes that can be attributed to a particular intervention, such as a project, program or policy, both the intended ones, as well as ideally the unintended ones.
en.wikipedia.org/wiki/Impact_evaluation

A type of outcome evaluation that focuses on the broad, long-term impacts or results of program activities. For example, an impact evaluation could show that a decrease in a community’s crime rate is the direct result of a program designed to provide community policing.
www.ojp.usdoj.gov/BJA/evaluation/glossary/glossary_i.htm

A form of outcome evaluation that assesses the net effect of a program by comparing program outcomes with an estimate of what would have happened in the absence of a program.
www.epa.gov/evaluate/glossary/i-esd.htm

Sometimes associated with the establishment of causal attribution between a development Activity and immediate, intermediate or longer-term outcomes or results.
nzaidtools.nzaid.govt.nz/evaluation-and-activity-cycle/definitions

measures the programs causal effect on the outcomes it seeks to achieve. The specific technique for estimating impacts varies according to the setting but all methodologies center on ways of constructing a plausible comparison or control group to establish the counterfactual.
www.absoluteastronomy.com/topics/Social_safety_net

a scientifically rigorous methodology to establish a causal association between programs and what they aimed to achieve beyond the outcomes on individuals targeted by the program(s).
www.globalhivmeinfo.org/DigitalLibrary/Digital%20Library/Glossary%20of%20Monitoring%20and%20Evaluation%20Terms.doc

It is usually undertaken at the end of an intervention to determine overall achievements in relation to the stated objectives. It attempts to establish a cause and effect relationship to show the extent to which the intervention has resulted in changing the circumstances of the target beneficiaries.
www.cop-mfdr-africa.org/forum/attachment/download

A study of the attribution of changes in the outcome to the intervention. Impact evaluations have either an experimental or quasi-experimental design.
www.3ieimpact.org/userfiles/file/Impact%20Evaluation%20Glossary.doc

Follow